Spectral convergence for high contrast elliptic periodic problems with a defect via homogenization

TL;DR

This paper investigates the spectral behavior of high contrast periodic elliptic operators with local defects, proving eigenfunction decay, strong two-scale convergence, and spectrum stability, thus linking microscopic perturbations to macroscopic spectral properties.

Contribution

It establishes the strong two-scale convergence of eigenfunctions and the spectral stability of high contrast elliptic operators with local defects, using homogenization techniques.

Findings

Eigenfunctions decay exponentially at infinity uniformly in epsilon

Eigenfunctions converge strongly in two-scale sense to homogenized eigenfunctions

Spectrum of the perturbed operator converges Hausdorff to the homogenized spectrum

Abstract

We consider an eigenvalue problem for a divergence form elliptic operator $A_\epsilon$ with high contrast periodic coefficients with period $\epsilon$ in each coordinate, where $\epsilon$ is a small parameter. The coefficients are perturbed on a bounded domain of `order one' size. The local perturbation of coefficients for such operator could result in emergence of localized waves - eigenfunctions with corresponding eigenvalues lying in the gaps of the Floquet-Bloch spectrum. We prove that, for the so-called double porosity type scaling, the eigenfunctions decay exponentially at infinity, uniformly in $\epsilon$. Then, using the tools of two-scale convergence for high contrast homogenization, we prove the strong two-scale compactness of the eigenfunctions of $A_\epsilon$. This implies that the eigenfunctions converge in the sense of the strong two-scale convergence to the eigenfunctions of a two-scale limit homogenized operator $A_0$, consequently establishing `asymptotic one-to-one correspondence' between the eigenvalues and the eigenfunctions of these two operators. We also prove by direct means the stability of the essential spectrum of the homogenized operator with respect to the local perturbation of its coefficients. That allows us to establish not only the strong two-scale resolvent convergence of $A_\epsilon$ to $A_0$ but also the Hausdorff convergence of the spectra of $A_\epsilon$ to the spectrum of $A_0$, preserving the multiplicity of the isolated eigenvalues.